I tried adding external media through both X and Facebook, both with post permalink or a picture url (in case you intended only graphic files to be media), but I always failed, either by receiving errors like No matching provider found or Could not retrieve the oEmbed resource or The provided URL does not represent a valid oEmbed resource, or, only in the case of an X status, the media seemed to have been loaded (with no Thumbnail though), but won't display after save (or actually it displays my own site in an iframe).
Here in this example the first is a SoundCloud link (with media_remote_audio module), last is Youtube, and middle two are X (Twitter) tweets (status):
No thumbnail:
No styling:
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